题目

 ―Hello! May I speak to Jack, please?    ―Yes, speaking.    ―Oh, I _________ your voice at first.   A. don’t recognize                            B. didn’t recognize   C. hadn’t recognized                           D. haven’t recognized 答案：B 说话的时候已经听出来是Jack的声音，“没听出来”是说话前的动作，用过去时。已知x＞0，y＞0，且（x+1）（y+1）=4，则有xy的最大值为（　　）A．1B．2C．3D．4